This invention relates to the deflocculation of clay slurries and more specifically to an improved method for the controlled deflocculation and reflocculation of clay slurries using an acetal carboxylate polymer.
Clays are generally considered by those skilled in the art to be plastic, soft, variously colored earths formed by the decomposition of aluminum minerals. In true clay, about 30 percent of weight of the solid particles have a diameter less than about 0.002 millimeters. Such clays are widely used for the manufacture of ceramics for industrial and domestic uses. Of the various clays, typical examples include quartz feldspar, kaolin, montmorillonite, siderite and the like.
In the mining of various clays, such as kaolin, the clay is contacted with water and a small amount of a deflocculating agent is added, such as tetraalkali metal pyrophosphate, alkali metal tripolyphosphate and the like, to form a thin slurry of the clay in water. The clay is normally reflocculated by the addition of a strong mineral acid and/or aluminum sulfate, thus reducing the pH of the slurry and causing the fluid slurry to reflocculate.
Although satisfactory results are achieved by the prior art processes, it has now been found that clays can be deflocculated and reflocculated as a function of time without the necessity of adding acid. The elapsed time between deflocculation and reflocculation is controlled by the selection of a particular acetal carboxylate polymer end group and the pH of the slurry. The polymers useful in the process of the present invention are known to the art and are described in U.S. Pat. No. 4,144,226 issued Mar. 13, 1979.
By contrast, prior art processes using alkali metal phosphates will deflocculate the clay slurry, and such phosphates will hydrolyze over a long period of time, permitting the clay slurry to reflocculate. However, reflocculation cannot be controlled as a function of time, but rather, an acid must be admixed with the slurry to lower the pH and reflocculate the clay. Now, according to the present invention, clays can be deflocculated and reflocculated over a period of time without the necessity of mixing acid to adjust the pH of the deflocculated clay slurry. It will be seen by those skilled in the art that a significant improvement has been made by the process of the present invention for the deflocculation and reflocculation of clays, since reflocculation occurs spontaneously but at a controlled rate. By the present process, the clay slurry can reflocculate, even in a quiescent state, permitting the clay slurry to be used in papermaking applications where agitation is used, or to cast the deflocculated slurry in a mold and then reflocculating in a quiescent state to form green ceramic ware for industrial and domestic applications.